Stevia is a genus of about 240 species of herbs and shrubs in the sunflower family (Asteraceae), native to subtropical and tropical South America and Central America.
The species Stevia rebaudiana Bertoni, commonly known as sweet leaf, sugarleaf, or simply stevia, is widely grown for its sweet leaves. The leaves have traditionally been used as a sweetener. Steviosides and rebaudiosides are the major constituents of glycosides found in the leaves of the stevia plant.
Stevia extracts generally contain a high percentage of the glycosides of the diterpene steviol. The leaves of stevia rebaudiana contain 10 different steviol glycosides. Steviol glycosides are considered high intensity sweeteners (about 250-300 times that of sucrose) and have been used for several years in a number of countries as a sweetener for a range of food products. Stevioside and rebaudioside A are the principal sweetening compounds and generally accompanied by smaller amounts of other steviol glycosides. The taste quality of rebaudioside A is better than stevioside, because of increased sweetness and decreased bitterness (Phytochemistry 68, 2007, 1855-1863).
The structures and chemical abstract service registry numbers for steviol and its glycosides that are the main sweetening agents of the additive steviol glycosides are shown below:
 CompoundnameC.A.S. No.R1R2 1Steviol471-80-7HH 2Steviolbioside41093-60-1Hβ-Glc-β-Glc(2→1) 3Stevioside57817-89-7β-Glcβ-Glc-β-Glc(2→1)  4Rebaudioside  A58543-16-1β-Glc  5Rebaudioside  B58543-17-2H  6Rebaudioside  C63550-99-2β-Glc  7Rebaudioside  D63279-13-0β-Glc-β-Glc(2→1)  8Rebaudioside  E63279-14-1β-Glc-β-Glc(2→1)β-Glc-β-Glc(2→1)  9Rebaudioside  F438045-89-7β-Glc 10Rubusoside63849-39-4β-Glcβ-Glc11Dulcoside A64432-06-0β-Glcβ-Glc-α-Rha(2→1)
Steviol glycoside preparations are generally white to light yellow powders that are freely soluble in water and ethanol. The powders can be odorless or have a slight characteristic odor. Aqueous solutions are 200 to 300 times sweeter than sucrose under identical conditions. With its extracts having up to 300 times the sweetness of sugar, stevia has garnered attention with the rise in demand for low-carbohydrate, low-sugar food alternatives.
Medical research has also shown possible benefits of stevia in treating obesity and high blood pressure. Because stevia has a negligible effect on blood glucose, it is attractive as a natural sweetener to people on carbohydrate-controlled diets.
Stevia sweeteners, for example, rebaudioside A (RA), one of the steviol glycosides, is regarded as a promising substitute of sugar, but it still has some drawbacks. When it is dissolved in an aqueous solution, there is a significant taste profile that differs from sugar, such as slow onset, bitterness and a lingering aftertaste. These drawbacks are some of the reasons that have resulted in unsatisfactory acceptable by consumers for stevia sweeteners, such as RA. The taste profile has become a key barrier to the use of stevia sweeteners in food or beverage applications, even if it has been approved as a food additive by the FDA. It is generally recognized that some impurities in stevia sweeteners are related to the aforementioned disadvantages. In recent years, a great deal of focus has been on obtaining a high purity of RA, from the initial 50%, 80%, 90% to the present 95%, 97%, 99%, up to 100%. However, with regard to 100% purity, sensory tests still show that a 200 ppm aqueous solution cannot bring a perfect taste close to sugar, and bitterness and aftertaste issues appear strongly at higher concentrations, for example, at a 500 ppm concentration. As a sweetener and as a promising sugar substitute, the taste of RA etc. must be further improved in order to meet sensory requirements for its applications in food and beverage, especially for use at high concentrations.
Therefore, a need exists for an improved stevia sweetener that overcomes one or more of the current disadvantages noted above.